1. Field of the Invention
The present invention relates to a camera system, and more particularly to a camera system having an arrangement that a conversion lens can be mounted/demounted with respect to a photographing lens of the camera.
2. Related Background Art
Conversion lenses which can be mounted/demounted with respect to a photographing lens of a camera are exemplified by tele-conversion lenses for lengthening the focal point distance, wide conversion lenses for shortening the focal point distance, and macro-conversion lenses (close-up lenses) for shortening the shortest photographing distance.
The tele-conversion lens is usually used to photograph sports scenes or wild animals and is used to obtain a telescopic effect when a remote object is photographed.
On the other hand, the wide conversion lens is used to obtain a wide-angle photographing effect, while the macro-conversion lens is used to approach an object which cannot be photographed by a photographing lens mounted on the body of the camera to obtain a larger photographing magnification.
If a range of the object distance which can be photographed is regarded, a tele-conversion lens, the size and the cost of which can be reduced, is provided by usually designing the tele-conversion lens such that satisfactory imaging performance can be exhibited when a focusing lens 1 of a photographing optical system composed of the focusing lens 1, a variator lens 2 and a relay lens 3 is used, as shown in FIG. 20, in only an extension range from an infinite photographing position to a predetermined position more adjacent to the remote side than the nearest photographing position. When the tele-conversion lens of a camera of the foregoing type is used, the photographing operation must be performed after the following fact has been confirmed: the object to be photographed is positioned more remote than a predetermined distance (for example, 3 m) which is more remote than a nearest distance (for example, 1 m) at which the photographing lens mounted on the body of the camera is able to photograph the object.
In order to use a macro-conversion lens, the design is so made that satisfactory imaging performance can be exhibited with the macro-conversion lens even if it is used in an extension quantity range from an infinite photographing position T to nearest end photographing position W as shown in FIG. 21. In this case, a macro-photographing effect can be obtained by designing the structure in such a manner that satisfactory imaging performance can be obtained even if the focusing lens 1 is further extended by a predetermined quantity than the nearest end photographing position W to be employed in an ordinary photographing operation.
If the focusing lens of the camera is so provided as to be capable of further extending by a predetermined quantity than the ordinary nearest end photographing position W, there is a fear at the time of using no macro-conversion lens that the focusing lens 1 is erroneously extended into a range which is allowed for the case where the macro-conversion lens is mounted. Therefore, a photograph, the image quality of which is unsatisfactory, can be taken due to the disorder of the aberration. Accordingly, an actual arrangement is so made that the focusing lens cannot be extended over an extension quantity allowed for a case where the conversion lens is not used even if the macro-conversion lens is mounted.
If the photographing lens, on which the conversion lens is mounted, is a zoom lens, the focal distance of the zoom lens is usually determined in such a manner that satisfactory imaging performance can be exhibited only when the zoom lens is used at a telescopic end or at a position adjacent to the telescopic end in order to provide a small and cost-reduced tele-conversion lens. In order to provide a small and cost-reduced wide conversion lens, the arrangement is usually made in such a manner that satisfactory imaging performance can be exhibited only when the zoom lens is used at a wide-angle end or at a position adjacent to the wide-angle end.
If a tele-conversion lens is used which is adapted to an instructed nearest distance which is made to be at a more remote position than the nearest distance which can be photographed by the photographing lens fastened to the camera body, there is a risk that an object is photographed at a shorter distance than the instructed distance due to leaving an operation of setting to the instructed nearest distance or to an error in eye-measurement. If the camera is operated ordinarily in this case, the taken photograph encounters deterioration in the image quality due to insufficient marginal illumination or disorder of the aberration.
If the macro-conversion lens is used, the photographing magnification is undesirably limited in order to prevent the foregoing erroneous use although a further high magnification photographing operation can be performed.
As for the focal distance of the zoom lens, a user sometimes photographs an object at another focal distance by using a tele-conversion lens designed to exhibit the optimum performance when it is used at only the telescopic end or at a position adjacent to the telescopic end or a wide conversion lens designed to exhibit the optimum performance when it is used at only the wide-angle end or at a position adjacent to the wide-angle end while leaving an operation of setting the zoom lens of the camera to the instructed focal point distances corresponding to the conversion lenses. If the camera is operated ordinarily in this case, the taken photograph similarly encounters deterioration in the image quality due to insufficient marginal illumination or disorder of the aberration.